• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.678-681
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• 1991

In this paper, we propose a robust linear time-invariant feedback compensator design methodology for multivariable system which have both matched and mismatched uncertainties. In order to attack the problem of designing robust compensators guaranteeing uniform ultimate boundedness of every closed-loop system response within an arbitrarily small ball centered at the zero state based solely on the knowledge of the upper norm-bounds of uncertainties, we use an approach based upon the comparison theorem which is an effective approach in studying augmented feedback control systems with both mismatched and matched uncertainties. Through the approach, we draw some sufficient conditions for robust stability, and we give a simple example.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.505-507
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• 2004

This paper attempts to compensate the nonlinearity between the input voltage and the output displacement of the piezoelectric stack in dynamic actuation by the following two ways. Firstly, the charge steering by circuit configuration reduces the hysteresis of piezoelectric actuator remarkably. However, it makes the ripple in positioning due to the phase lag and noise induced from the elements of the long closed loop. Secondly, the feedforward control by neural network compensates the hysteresis of the piezoelectric actuators effectively with the appropriate selection of the input variables for the training. The improvement of the dynamic performance of the piezoelectric actuators by the developed linearization technique is verified by experiments.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.1
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• pp.168-175
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• 2010

The issue of rejecting periodic disturbances arises in various applications dealing with rotating machinery. A new method using DIDF (Dual-Input Describing Function) is presented for the rejection of periodic disturbances with uncertain frequency. This can be added to an existing feedback control system without altering the closed-loop system stability. The objective is to design a nonlinear compensator to secure specified oscillation amplitude and frequency which are the same as disturbances. We suggest two procedures to determine coefficients for DIDF's synthesis. The structure of the proposed DIDF is so simple that we can easily synthesize. A number of computer simulations were carried out to demonstrate the salient feature of the proposed DIDF compared to the conventional ones(that is, adaptive algorithms).

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.600-603
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• 2007

We propose a method to estimate the asymptotic stability region(ASR) of a mismatched uncertain variable structure system with a bounded controller. The uncertain system under consideration may have mismatched parameter uncertainties in the state matrix. Using linear matrix inequalities(LMIs) we estimate the ASR and we show the quadratic stability of the closed-loop control system in the estimated ASR. We also give a simple LMI-based algorithm for estimating the ASR. Finally, we give a numerical example in order to show the effectiveness of our method.

• Proceedings of the KIEE Conference
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• 2008.10b
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• pp.462-463
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• 2008

This paper proposes a method for dynamic output-feedback controller design for stochastic time-delay systems. Based on recent results on time-delay systems control, a tractable and delay-dependent design condition is proposed, which provides a dynamic output-feedback controller to render the closed-loop stochastic time-delay systems to be asymptotically stable in the mean-square sense. The feasibility problem of the proposed condition is recast into a cone complementarity problem. An algorithm adopting cone complementarity linearization is presented to solve the resulting problem.

• Journal of Power Electronics
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• v.1 no.1
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• pp.1-8
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• 2001

The elimination of a pole sensor is desirable due to the low-cost requirement, the compactness, and the applied drives. This paper proposes the algorithm for the initial pole-position estimation of a surface permanent magnet linear synchronous motor (PM-LSM), which is carried out under the closed loop control without a pole sensor and is insensitive to the motor parameters. This algorithm is based on the principle that the initial pole position (IPP) is estimated by the trigonometric function of the two reference currents. The effectiveness of the proposed algorithm is confirmed by testing a surface PM-LSM with large disturbance, which result shows that IPP is well estimated within a satisfied moving-distance and a shorter estimation taken-time even if large disturbance such as cogging and friction is existed.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1235-1244
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• 2018

The application of shunt capacitor banks and underground cables typically induces resonance in power distribution systems. In this study, the propagation of resonance in a microgrid (MG) with inverter-based distributed generators (IBDGs) is investigated. If resonances are not properly damped, then the output current of the inverters may experience distortion via resonance propagation due to the adverse effect of resonances on MG power quality. This study presents a conceptual method for identifying resonances and related issues in multi-inverter systems. For this purpose, existing resonances are identified using modal impedance analysis. However, some resonances may be undetectable when this method is used. Thus, the resonances are investigated using the proposed method based on the frequency response of a closed-loop MG equivalent circuit. After analyzing resonance propagation in the MG, an effective virtual impedance damping method is used in the IBDG control system to damp the resonances. Results demonstrate the effectiveness of the proposed method in compensating for existing resonances.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.1
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• pp.109-116
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• 2008

Model matching problem of asynchronous sequential machines is addressed in this paper. The main topic is to design a corrective controller such that the closed-loop behavior of the asynchronous sequential machine can follow a given model, i.e., their models can be "matched" in stable states. In particular, we assume that the considered asynchronous machine suffers from the presence of an input disturbance that can cause undesirable state transitions. The proposed controller can realize both model matching and elimination of the adverse effect of the input disturbance. Necessary and sufficient condition for the existence of a corrective controller that solves model matching problem is presented. Whenever controller exists, algorithms for their design are outlined and demonstrated in a case study.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.10
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• pp.1854-1860
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• 2008

In this paper, we deal with the problem of delay-dependent robust and non-fragile stabilization for descriptor systems with parameter uncertainties and time-varying delays on the basis of strict LMI(linear matrix inequality) technique. Also, the considering controller is composed of multiplicative uncertainty. The delay-dependent robust and non-fragile stability criterion without semi-definite condition and decomposition of system matrices is obtained. Based on the criterion, the problem is solved via state feedback controller, which guarantees that the resultant closed-loop system is regular, impulse free and stable in spite of all admissible parameter uncertainties, time-varying delays, and controller fragility. Numerical examples are presented to demonstrate the effectiveness of the proposed method.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.1
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• pp.45-51
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• 1999

Thermal expansion of the ball screw can directly affect the accuracy of positioning along the travel axis in the semi-closed loop type CNC Lathe. In this paper, use of MACRO variables can make the thermal displacement of the ball screw estimated. Also, the estimated displacements of the ball screw are controlled by calculating the interval of pitch error rate in the Numerical Control(NC). Under the constant operating conditions, the thermal expansion of the ball screw was measured to confirm the effectiveness of the compensation method in the CNC Lathe. By using this method the results show that the thermal displacement of the ball screw could be reduced to 20% compared with ordinary method.